The RNG with cards does kinda bulls things up when trying to put SCH and AST against each other DPS wise. I think party compo is going to be a consideration whether AST is good to take with or not due buffs really only benefiting certain classes, where cards like arrow are more beneficial for some as oppose the speed boost. Also dps wise SCH and AST are close and SCH will only more if they use their stacks for ED, however they do more DOT damage whereas AST does less DOT damage but more filler damage.

If the other healer can handle the majority of things and you can stand there in dps stance for prolonged periods of time. However if that is the case it might be worth going double WHM one heals other does predominantly DPS lol